Mental health and relationships

Mental disorders are among the largest causes of lost health worldwide. In 2019 they accounted for 125.3 million disability-adjusted life years (a combined measure of years lived with illness and years lost to early death), 4.9% of the global total, and remained among the ten leading causes of disease burden [1]. They also shorten life. A 2015 meta-analysis (a study that pools the results of earlier studies) of 148 studies found that people with mental disorders had 2.22 times the mortality (risk of death) of comparison populations, with a median of 10 years of potential life lost, and that 67.3% of their deaths were from natural causes such as heart and lung disease rather than from suicide or injury [2]. Estimated losses range from 7 to 11 years for depression to 9 to 24 years for substance use disorders [3]. These figures are described under Mental health conditions and lifespan.

Long-term stress and emotional strain are linked to mortality even below the level of a diagnosable disorder. In pooled data on 68,222 adults in England, mild psychological distress was associated with 20% higher mortality and high distress with 94% higher mortality [4]. The physiology of stress, its links to heart disease and working hours, and the trials of stress management are covered under Stress and anxiety. Some of the strongest associations in the section begin in childhood: in a US survey across 25 states, 15.6% of adults reported four or more adverse childhood experiences such as abuse, neglect or serious household problems [5], and four or more such experiences are associated with higher odds of every adult health outcome examined, from smoking and heart disease to depression [6].

Relationships are the other half of the section. Across 148 studies and 308,849 participants, people with stronger social relationships had 50% higher odds of survival over the follow-up periods studied [7], and social isolation, loneliness and living alone were each associated with 26 to 32% higher mortality [8]. These studies are summarised under Social connection. Pet ownership, particularly dog ownership, has been studied as a source of both companionship and physical activity: owners of dogs had 24% lower all-cause mortality (death from any cause) in pooled studies that were not adjusted for other differences between owners and non-owners [9], while a European study of 23,274 older adults that accounted for these differences found no significant association for any type of pet [10]. Nearly all evidence in this section is observational (it comes from tracking people rather than assigning them to groups), so illness, income and other shared factors may explain part of each association.